The present invention relates to a rotary apparatus on which a working tool such as a grindstone is mounted.
A rotary apparatus having a spindle rotatably supported by magnetic attraction in a non-contact condition has the following advantages: the apparatus can be used in a vacuum; the loss or wear rate of a bearing is low; lubricating oil is not required; no noise is made; and maintenance-free operation is ensured.
As shown in FIG. 3, in the rotary apparatus, the front end portion 31 of a rotary spindle 30 penetrates the front wall of a shell 32, thus projecting from the shell 32 to the outside; the spindle 30 supported by radial bearing sections 33 and a thrust bearing 34 both provided in the shell 32 is driven by a driving section 35; and a working tool 36 such as a grindstone is mounted on the front end portion 31 of the spindle 30. The working tool 36 is mounted on the spindle 30 at a position spaced a predetermined distance from the front wall of the shell 32 and the working space of the working tool 36 is provided in the axial direction of the spindle 30.
Radial sensors 37 and 38 for detecting the positions of the spindle 30 in the radial direction are provided in the front and rear of the shell 32, respectively, to prevent deviation of the spindle 30 from the axis thereof. A thrust sensor 39 for detecting the position of the spindle 30 in the thrust direction thereof is provided in the inner surface of the rear wall of the shell 32.
However, according to the above-described conventional construction, since the front wall of the shell 32 is interposed between the radial sensor 37 inside the shell 32 and the front end portion 31 of the spindle 30 outside the shell 32, there is a great difference between the spindle deviation from the axis of the spindle 30 detected by the radial sensor 37 and the deviation of the front end thereof. Therefore, it is difficult to control the radial position of the spindle at the front end portion 31 thereof accurately.
Additionally, according to the conventional rotary apparatus using a magnetic bearing, since the radial sensors 37 and 38, the radial bearing 33, the thrust sensor 39, the thrust bearing 34, and the driving section 35 are provided in the shell 32 along the axis of the spindle 30, the axis of the spindle 30 of the rotary apparatus using the magnetic bearing is longer than that of the spindle of a rotary apparatus using a fluid bearing. Since the natural frequency of an axis is inversely proportional to its length, the natural frequency of the spindle of the apparatus using the fluid bearing is small. Therefore, according to the above-described conventional construction, the spindle has a resonance in a region in which the number of rotations thereof is low. As such, it is difficult to increase the number of rotations (i.e. the rotational speed) thereof.